It’s important to distinguish this from previous criticisms, which as you rightly point out have been despicable smears. However the issue of the SWP covering up rape and sexual assault has actually been raised from left wing organisations (including BAME and women’s groups), and in fact from many staunch Corbyn supporters.
An earlier version of this open letter was initially addressed to several of the headline speakers, it has since been…mediadiversified.org
I certainly don’t think the PLP give two hoots about any of this, other than that it gives them a new stick to try and cynically beat Corbyn with.
I’m not going to try and argue that attending a SUTR rally is equivalent to endorsing the SWP’s toxic internal culture — you have laid out your legitimate objections to this already. But I think it is worth acknowledging that there is a definite problem with the latter organisation, and that many of those objecting to Jeremy Corbyn (and other highly respected Labour MPs’) attendance of the former are doing so in good faith.